my baxi 105e instant boiler is operating properly and hot water is available but the heating system is losing all pressure with no apparent leaks anywhere-what could be the problem? The heating system will operate until all pressure is lost, all radiators have been bled and are full.

paul reid, September 2007

have you checked to see if your pressure relief valve is leaking, this will be outside (the outlet) usually a small copper pipe faced back to the wall, or it could be the expansion vessel, to check this you need to de-pressurize the system and check the vessel pressure on the schraeder valve (a car tyre pressure tester will do the job), it should be about 1 bar or 14 psi, it can be re-pressurized using a car footpump or similiar, another way to test is tie a plastic bag around the pressure relief outlet and check after the heating has been running for a day or so if the bag is full of water the pressure vessel is deflated.

tojo, September 2007